In the case of extracorporeal blood treatment, for example, hemodialysis, the blood to be treated flows in an extracorporeal blood circuit through the blood chamber of a dialyzer divided by a semipermeable membrane into the blood chamber and a dialyzing fluid chamber, whilst in the case of a dialyzing fluid system dialyzing fluid flows through the dialyzing fluid chamber. The extracorporeal blood circuit has an arterial hose line which leads to the blood chamber, and a venous hose line which leads away from the blood chamber. The known hemodialysis apparatuses have a blood pump which is generally arranged upstream of the blood chamber of the dialyzer in order to ensure an adequate flow of blood in the extracorporeal blood circuit.
Great technical demands are made on the blood pump. Only certain types of pump therefore come into consideration. Hose pumps that convey the patient's blood through the arterial and venous hose line have been tried and tested in practice.
According to their mode of operation, hose pumps are also referred to as peristaltic pumps, The pump action is based on the fact that at least one occlusion moves along the elastic hose line serving as the pumping space and thereby displaces the enclosed fluid in the delivery direction.
With the most common design of hose pumps, the adjustment takes place in such a way that the elastic hose is completely occluded at the moved constriction points. These pumps arc therefore also referred to as occlusive hose pumps. The moving constriction points or occlusions that transport the blood in the pump hose can be generated in various ways from the technical standpoint.
Roller pumps are known, wherein the hose is inserted between a stator, which forms a curved roller path as a counter-bearing, and a rotor mounted rotatably therein and fitted with rollers, so that the rollers roll off on the hose in the delivery direction. The rollers may be spring-mounted on the rotor, so that they exert a pressing force on the hose. Finger pumps are also known, wherein the constriction points or occlusions are produced by a series of mobile stamps (fingers) arranged along the hose.
An overview of the various designs of roller and finger pumps is given in Dialysetechnik, 4th edition, Gesellschaft für angewandte Medizintechnik m.b.H. & Co. K G, Friedrichsdorf, 1988.
Electric peristaltic hose pumps are used in the known blood treatment apparatuses not only for conveying the blood, but also for conveying other fluids. Great demands are made on the proper operation of such hose pumps when they are used in medical-technical apparatuses, in particular in blood treatment apparatuses.
During the operation of roller pumps, the problem arises that a complete occlusion of the hose line is no longer produced when there is an increase in the flow resistance. On the contrary, the rollers begin to rise from the hose line. In this case, proper operation of the roller pump is no longer ensured.
U.S. Pat. No. 5,629,871 describes a method and a device for the monitoring of the functional capability of individual subassemblies of a hemodialysis apparatus. These also include hose pumps, whereby the pump current or the voltage is monitored in order to deduce the functional capability of the pump. It is known from U.S. Pat. No. 4,781,525 to use the pump current to determine the delivery rate.
WO 97/45150 describes a method for the determination of the delivery pressure of a pump, wherein the pump current is determined. Since deviations from a linear relationship between the delivery pressure and the pump current can occur under certain circumstances, the use of a calibration curve is proposed.
The problem underlying the invention is to provide a method and a device for the operation of an electric peristaltic hose pump, in particular the hose pump of an extracorporeal blood treatment apparatus, which respectively permit reliable monitoring of the proper operation of the hose pump.